On v9.0.1, I get 37.8958. What version are you using? Run "ReleaseID" /. ("Kernel" /. SystemInformation["Small"])
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rcollyerAug 8 '13 at 16:27

Hm! I get 8.0.1.0 (2063990, 2063802). Note: I tried restarting the program and get the same negative answer.
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jorgenAug 8 '13 at 16:30

1

I confirmed I get that answer on 8.0.1, but I don't get it on v9. So, it is likely a bug in v8. Although, I haven't tried v8.0.4. My only advice: upgrade.
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rcollyerAug 8 '13 at 16:36

Thanks for advice! Note: it seems to me the answer you get must also be wrong, since the function and sine are both too small on the interval to give 38 (try plotting it)
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jorgenAug 8 '13 at 16:37

1

Hmm, I hadn't paid attention to that. NIntegrate gives an answer I'm comfortable with (0.13956), and it works fine on v8.0.1, too. So, I'd use that, especially considering the coefficients in your function have vastly different scales, and may be confusing things.
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rcollyerAug 8 '13 at 16:48

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